Pros: - Work on what you like, with the people you like - Potentially very high salary, definitely more than you would get as an employee - Want to work on side projects (e.g., software, books, and courses)? Go for it, and benefit from multiple income streams.
Cons: - You're running a business. That requires time, as well as skills/knowledge (often learned the hard way) that are completely separate from programming. - You have to market yourself (until you're good enough that people contact you). No marketing, no work. No work, no salary. - It's harder to do when you're married and have children. (I started when I was single.)
In many ways, freelancing is like the "founder" described in the article. However, the article also talks about teammates and a financial plan (including funding). Plenty of successful freelancers make good money just by themselves (or maybe 1-2 junior people). And I definitely never intend to take investment money.
Not everyone is cut out to be a freelancer. But it's a very viable option, beyond being a founder, executive, or employee. And I can tell you that many of the founders, executives, and employees I meet as I travel the world teaching Python are quite jealous of my satisfaction.